1. Field of the Invention
The present invention relates to means for isolating vibration or shock; more particularly the present invention relates to a novel means for isolating the vibration or the shock of a loaded housing from a support means for the loaded housing owing to provision of a circular displacement in the loaded housing, in which the loaded housing such as a loaded body supported by a shaft means is supported rotatably about an axis which can move along a circular path about a line parallel to said axis of rotation, whereby vibration or shock can be prevented.
For the purpose of the present invention, the wording "loaded housing" can be defined as a load bearing body which is supported through a shaft means. Thus, the loaded housing here may include members, such as, for example, a piston, a swing arm, a roll, a roller, a pulley, an impeller, a toothed wheel, a milling cutter, a grinding wheel, a flywheel, a dozer blade or a bucket of an earth-moving construction machine, and a wheel of a vehicle.
2. Description of the Prior Art
From the view point of a dynamics, a motion of a rigid body may be classified into two modes, that is, translation and rotation. A mechanical vibration may be divided into two categories, that is, a linear vibration system and a rotational vibration system. In this case, the rotational vibration system corresponds to the rotation and the linear vibration system corresponds to only the linear motion which is a branch of the translation. Accordingly, although a conception as to a circular vibration system corresponding to the rotation which is one mode of the translation must be made the subject matter of study, in the past, the result of such study has scarcely been published.
In a conventional method for supporting a loaded housing, a bearing unit is employed between the loaded housing and a shaft supporting it. In such a conventional structure, since most bearing means have only freedom of rotation, such structure has defects in that the bearing means simply supports the rotatably or swingably loaded housing, vibration or shock on the loaded housing being directly transmitted, without being almost absorbed to a support housing holding the shaft through bearing means. Hithertofore, in order to prevent or absorb vibrations or impacts, it has been a common practice to insert a resilient material such as rubber or synthetic resin into a bearing mount, that is, between a bearing outer race and the housing or, in view of obtaining a good heat diffusion, to dispose a metallic spring, so that the housing is given another freedom of movement.
However, in view of the nature of the rotational movement, the following conditions have to be met in order that the housing is given another freedom of movement. First of all, in a resiliently supported housing, when it is displaced in response to vibrations or impacts applied thereto, the center axis of a mating hole formed in the housing for receiving a bearing must be maintained parallel to the center axis before it is displaced and the axis shall not be displaced in the axial direction. If this condition is not met, and if an angular displacement to the center axis of the mating hole is created, an angular momentum of the rotation is varied, and such variation of the angular momentum will disturb the rotation or swinging movement of the housing with the result that a smooth movement of housing is interrupted. Also, if the axial displacement is created, an additional thrust component will be created.
Secondly, the center axis of a mating hole formed in the housing for receiving a bearing must always be parallel to the center axis of the bearing throughout the displacement of the housing. If this condition is not met, a twist will be induced between the bearing and the shaft supported, thereby, resulting in an excessive concentrated stress. Therefore, the bearing is excessively damaged and its life is reduced.
Thirdly, the position of the loaded housing has to be easily and accurately determined irrespective of the amount of load on the housing. Since the loaded housing is accompanied with rotational or swinging movement, it is usual that the position thereof is precisely determined. For this reason, in order to facilitate assembling of a machine, the deflection of a resilient mount supporting a bearing must be accurately determined irrespective of the load on the housing.
It is impossible in principle to satisfy all of the above requirements simultaneously, preventing or absorbing vibrations or impacts by means of the aforementioned resiliently supported bearing.
Further, disadvantages of the prior art will be described hereinafter with reference to a support system of a wheel which is also a kind of a loaded housing. A conventional method for supporting a wheel include the type in which the wheel is only rotatable about the axis thereof such as in a bicycle, and another type, a so-called linear vibration system in which the wheel is rotatable about the axis thereof and, at the same time, vertically movable to absorb vibration and impacts transmitted from the wheel to a frame, the vertical movement of the wheel being resisted by a spring or a damper, as in an automobile, an aircraft, and a railway car. In any event, this method for supporting a wheel cannot provide any effect for absorbing longitudinal impacts.
Impacts encountered during aircraft landing will now be discussed. During landing, an aircraft is subjected to a shock load which is caused by a collision of the wheels onto the run-way and which is dependent on the rate of descent of the aircraft, and an acceleration shock load which is caused by the fact that the wheels are abruptly accelerated to a rotating speed corresponding to the horizontal speed of the aircraft.
Riding comfort is improved since the vertical vibrations or shocks on the car body can be remarkably reduced, however, there is no effect in absorbing longitudinal shocks or impacts. Therefore, a conventional suspension means is neither effective for absorbing longitudinal impacts such as those encountered during head-on collision or rear-end collision between cars or during car coupling operations, nor effective to prevent longitudinal shocks such as those experienced when a car to runs along an uneven surface, and during sudden start or sudden stop which often causes passengers to fall one on another in a railway train.
Further, an aircraft is subjected to an impact during landing due to an engagement with the surface of a runway. Moreover, it also has a problem in respect of safety during landing and expenses for operation due to the fact that wheels provided in landing gears are abruptly accelerated to a rotating speed corresponding to the horizontal running speed of the aircraft accompanied with heavy slippage between tires and the runway and remarkable tire wear.
Nowadays, it is possible to absorb vertical shocks acting on an aircraft during landing by using complicated and expensive damping means; however, there is no practical means for absorbing acceleration shocks on wheels. Thus, the acceleration shock loads are usually accommodated by increasing the strength of the wheels. However, this does not solve the basic problem and brings about several difficulties such as increased wheel costs, possible wheel skids due to the existence of rubber material adhered on the runway during previous landings, and increased operational costs due to frequent replacement of wheels.
Further problems in vibration prevention or shock absorbing technique to which the present invention is applied will now be discussed.
Automobile accident involves very serious problems since drivers or other persons are injured and their lives are often lost through an accident. For this reason, it is now required that automobile seat belts and head restraints be provided. Among these, seat belts are used to prevent a so-called secondary collision in which an operator or passengers are forwardly thrown away from their seats towards a portion of the car body. Thus, the elongation of the seat belt must be limited within a predetermined maximum value which is determined by the space in the car body. However, one problem is that, since the belt elongation is closely related to damping characteristics, it is undesirable to simply reduce the value of belt elongation. When the belt elongation is limited to an excessively small value, the shock load on the car body will be transmitted to the passengers without being absorbed. Further, since only the bodies of the passengers are rigidly restrained in their seats, their head portions will abruptly be displaced with the result that neck portions are locally stressed and injured.
Therefore, it is essential in designing a seat belt to clearly determine the elongation of the belt from the view point that both prevention of the secondary collision and absorption of shock loads transmitted to passengers are balanced. Nevertheless, these points are not sufficiently taken into account.
On the other hand, a head restraint is used to prevent a passenger from being damaged at his neck portion upon rear end collision. However, the head restraint is not effective to restrain the movement of the passenger's head unless the head is located very close to the restraint. Thus, neck muscles cannot follow an abrupt movement of the head, and the human body is thrust forwardly leaving the head as it was causing an unusual posture which may create an excessive shear force, bending moment or tensile force at the neck portion.
From the above discussion, it will be noted that safety provisions against automobile accident are not satisfactory in respect of absorbing shock loads on a car body before the loads are transmitted to the passenger. A prior shock absorber has been ordinally constructed on the principle that the kinetic energy of one moving member is gradually absorbed and that a rapid change of velocity thereof has been eliminated by provision of the absorber in the face of a solid wall or other moving member upon collision of a moving member with the solid wall or other moving member. However, the absorber has the defect that the production of impacts therebetween may not be avoided, if the kinetic energy of the moving member is large and the efficiency of absorption of the shock of the absorber is below this kinetic energy.
According to a known machine, a resilient material such as vibration absorbing rubber is inserted between a vibration generating machine and a foundation thereof. However, in a machine such as a vacuum pumps, a centrifugal separator, or a drying machine in which a horizontal vibration is considerably generated as the horizontal vibration is always accompanied by rotational vibration, so that it is required to determine the natural frequency of both the horizontal and the angular vibration sufficiently lower than the frequency of the machine. In order to satisfy these requirements, it is necessary to select a resilient material having substantially lower coefficient of resiliency in the vertical direction. Thus, the support of the machine will become unstable and practically impossible to absorb vibration.